GEOMORPHOLOGICAL CONTROLS ON POST-FIRE DEBRIS FLOW YIELD RATES IN THE GRIZZLY CREEK BURN AREA

Runoff-initiated debris flows are those that typically do not initiate with liquefaction of a landslide mass, and are characterized by volume increase along the flow path as material is mobilized by the flow. The amount of material mobilized is quantified as a yield rate, in units of volume per unit length of channel. Previous research has identified critical thresholds where post-fire debris flow yield rates can abruptly increase by over 100%, significantly changing the volume and hazard of debris flows. We highlight a workflow which has been developed to identify and measure changes in channel erosion and deposition patterns. This workflow is used to locate yield rate thresholds and other sediment flux patterns at multiple burn areas in the western United States. Implemented in the Grizzly Creek Burn Area, near Glenwood Springs, CO, this workflow is used to analyze the influence of geomorphometric, hydrologic, and burn severity parameters on the location and magnitude of identified yield rate thresholds.

Geomorphometric features including channel gradient, catchment area, knickpoint presence, and channel width play a crucial role in controlling debris flow processes and evolution. These geomorphometric factors interact with critical zone hydrologic processes and open channel flow dynamics to modulate the initiation and propagation of debris flows. By examining these features in conjunction with burn severity, we can better understand the spatial variability in debris flow behavior across different post-fire landscapes. This research aids in advancing our understanding of the driving processes and intra-channel evolution of debris flows, and how they may differ across different regions in the western United States. The broader implications include a more comprehensive knowledge of hazard magnitude and improved mitigation strategies, thereby enhancing our ability to predict and manage debris flow hazards effectively.